The geometry and numbering logic is separate to the dialog, and
can be separated for clearer logic and better testability.
Moreover, refactor it to avoid any dependency on pcbnew
classes, so it can be move to common for potential re-use in
eeschema and friends in future.
Also convert all wxPoint logic in these classes to VECTOR2I and
fix some function visibilities.
Add some unit tests of the ARRAY_OPTIONS geometry and numbering.
Devolve the logic as to whether a pad should be numbered or not
to a pad utility function. Add a very simplistic test for this
function (demonstrating how to test BOARD_ITEMs in general).
Fixes: lp:1804787
* https://bugs.launchpad.net/kicad/+bug/1804787
